The present invention pertains to the extraction and delivery of an AC signal imposed on a DC power conductor in the context of power line communication functions in heavy duty tractor and trailer combinations. More particularly, it pertains to a way to efficiently wire a truck tractor for delivery in the tractor of a signal, such as a lamp illumination signal, indicative of a malfunction of a trailer automatic braking system, which signal originates as an AC signal transmitted to the tractor over a selected DC power conductor coupled to the tractor via a standard 7-wire connector.
Attached hereto as Appendix A is Standard SAE J560, which is incorporated by reference hereinto.
For several years now, a consortium of companies have been working to meet a National Highway Traffic Safety Administration (NHTSA) mandate to provide a warning lamp in the cab of a tractor that notifies a driver of any tractor and/or trailer anti-lock brake system (ABS) malfunctions. This task initially seemed too much for traditional J560 connectors, a seven-pin connector that has been specified by the Society of Automotive Engineers (SAE), that link tractors and trailers because all seven pins of the connector were already being used to power various functions on the trailer. To remedy this problem, a number of options were suggested, including using a second J560 connector and a revised connector with more pins, but neither of these options were readily accepted by the trucking community. As a result, the PLC4Trucks (PLC) system, a computer controlled system that allows one wire to provide power for multiple functions, was developed. Trucks that incorporate the PLC system enable trailer manufactures the ability to comply with the NHTSA mandate.
The Maintenance Counsel of the American Trucking Association accepted the PLC system as the industry standard xe2x80x9ctractor-trailer communication interfacexe2x80x9d in 1998. The PLC system utilizes a multiplexing device, which uses power-line carrier technology to send signals along a wire already carrying power for another use, signals the driver of any malfunction in the ABS of a trailer he is pulling, while also allowing control of other trailer accessories. Central to the PLC system is the Intellon P485 chip, a xe2x80x9cchirping chipxe2x80x9d designed by Intellon, which emits a very distinct signal and serves as the brains of the PLC system. The chip is generally located in the electronic control module of the trailer ABS equipment.
PLC systems use the auxiliary circuit (the xe2x80x9cblue wirexe2x80x9d) of the J560 connector to send messages between electrical transceiver modules located on the tractor and the trailer. The system uses the P485 chip to send a PLC signal or (chirp) from the trailer ABS electrical module that can be recognized or understood by an ABS transceiver on the tractor. When the transceiver on the tractor identifies the signal, it responds. In the case of trucks implementing the PLC system, the response is one of only two thingsxe2x80x94turn the tractor ABS status light on or turn it off. The light will stay on as long as a problems in the ABS persist and will go out if the problem stops, is fixed or if the trailer is unhooked from the tractor. The malfunction light is located in the tractor instrument panel and indicates a malfunction in the trailer""s ABS.
While the PLC system provides many benefits, the same auxiliary circuit used by the PLC system to transmit PLC signals to power the trailer ABS has previously been used by many truck operators to power and operate lights, pumps, lift-gates and other devices on the trailer. Thus, as PLC signals are transmitted across the auxiliary circuit, the high frequency signals may be transmitted back to the power supply system of the tractor. If a PLC signal gets into the power supply system of the tractor, it can cause interference with electronic instruments inside the tractor cab. In order to prevent this, there is a need for a device which isolates the high frequency PLC signals applied on the trailer power supply system and prevent them from appearing in the power supply system of the tractor cab, the tractor and trailer power supply systems are linked when the trailer is connected to a trailer via electrical connectors conforming to SAE standard J560. Such a device must be cost-effective and easy to implement into existing tractor/trailer combinations.
The present invention is generally directed to low-pass filter connectable between a selected pair of DC power lines in a truck tractor to isolate an AC signal present on one of the selected power lines from other DC power lines in the tractor, and to present the AC signal to the other one of the selected power lines. All of the DC power lines are connectable to a battery in the tractor. Each of the pair of DC power lines are associated with one of an AC signal generator, an AC signal receiver, and an AC signal transceiver. The filter comprises a pair of inductors connectable in the first and second power lines so that each inductor has a battery end and an opposite end. The filter further includes a capacitor connected between the opposite ends of the inductors.
In a preferred embodiment, the filter comprises a first power line carrying DC power connected between the tractor battery and a tractor ABS transceiver. The filter also includes a second power line carrying DC power connected from the tractor battery to a tractor connection to a trailer ABS module. A first inductor is coupled in the first power line between the tractor battery and the tractor ABS module to block the passage of AC signals from the tractor ABS to the tractor battery, but permit the passage of DC current from the tractor battery to the tractor ABS transceiver. A second inductor is coupled in the second power line between the tractor battery and the tractor connection to block the passage of AC signals from the trailer ABS module to the tractor battery but permit the passage of DC current from the tractor battery to the trailer ABS module. A capacitor is coupled between the first and second power lines for communicating AC signals between the tractor ABS transceiver and the trailer ABS transceiver. An additional pair of capacitors are connected between the first and second power lines and frame ground to maintain the passage of pure DC power along the power lines between the tractor battery and the low-pass filter.
The present invention provides an improved method for preventing high frequency signals from appearing in the power supply system of the tractor and interfering with electric instruments inside the tractor cab.